Growth and microclimate of "Essex" soybeans as affected by rowspacing

Author

Paul Brewer Francis

Date of Award

8-1985

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

W. L. Parks

Committee Members

Otto Schwarz, John Reynolds, Russel Lewis

Abstract

"Essex" variety of soybeans, [Glycine max, L. (Merr.)], were planted on Sequatchie loam, (fine-loamy, siliceous, thermic Humic Hapludult), in rowspacings of 25-, 38-, and 51-cm with or without a wheatstraw mulch in 1983, and 13-, 25-, 38-, 51-, and 76-cm with no mulch treatment in 1984 with irrigation being used both years. Micro climate, plant growth, and water use data were collected throughout the growing season. Canopy CO₂ concentrations, ([CO₂]), in the upper half of canopy were around 320 μL⋅L^-1 at midday as compared to 340 μL⋅L^-1 at a reference height, six meters above ground. At night, the [CO₂] exceeded 500 μL⋅L^-1. Lower [CO₂] were observed in the narrow rows (13 and 25cm) at midday and higher levels were present for short periods after dusk. This was thought to be due to leaf density, which was higher in the upper strata of the narrower rows. In the narrower rows, no horizontal deviations in [CO₂]]were observed. The [CO₂] was 5 to 15 μL⋅L^-1 lower between the row middles at midday than over the row of the 76cm treat-ment. Mulching had no effect on the [CO₂]. Soil CO₂ emissions among treatments were similar and averaged around 144 kg⋅ha^-1⋅day^-1 Soil temperatures across treatments were similar except during midday, (1500 to 1900 hour), where it was in excess of 32C in the row middle of the widest rowspacing. After mid-pod fill growth, rowspacing effects on soil temperatures were absent. Mulching cooled the top 5cm of soil two to five degrees at midday up to the pod-filling stage of growth, thereafter no differences were observed. Apparent evapotranspiration was significantly lower in the narrowest rowspacings at canopy closure. Prior to and after, there were no treatment effects. Values ranged from 0.50 to 0.70cm H₂O⋅day^-1. Rowspacing had no effect on average seed weights or seeds per pod. Total seed production per plant increased with rowspacing. Net assimilation rate and relative growth rate decreased proportionally with rowspacing and the leaf area ratio was constant across treatments. After early pod fill, the leaf area index across treatments was similar.

Recommended Citation

Francis, Paul Brewer, "Growth and microclimate of "Essex" soybeans as affected by rowspacing. " PhD diss., University of Tennessee, 1985.
https://trace.tennessee.edu/utk_graddiss/7802